Emission of nitrous oxide and carbon dioxide and dynamics of mineral N in wastewater sludge, vermicompost or inorganic fertilizer amended soil at different water contents: A laboratory study

Liming or vermicomposting eliminates pathogens from wastewater sludge, but might affect CO₂ and N₂O emissions when added to soil. Soil incubated at 40%, 60%, 80% and 100% of its water holding capacity (WHC) was amended with limed or unlimed wastewater sludge, vermicompost or inorganic fertilizer, while emissions of N₂O and CO₂ and mineral N concentrations were monitored in aerobic incubation experiment for 7 days. Application of unlimed wastewater sludge significantly increased the emission of CO₂ compared to the unamended soil, but not the other treatments except when unlimed wastewater sludge was added to soil incubated at 60% WHC. The emission of CO₂, was generally largest in soil incubated at 60% WHC and lowest in soil incubated at 100% WHC. The emission of N₂O after 1 day was significantly larger in soil amended with unlimed wastewater sludge compared to the other treatments, but not when soil was incubated at 100% WHC. The emission of N₂O increased with increased soil water content. The concentration of NH₄⁺ was largest in soil amended with limed or unlimed wastewater sludge and lowest in the unamended soil and soil water content had no clear effect on it. In soil incubated at 40%, 60% and 80% WHC, the largest amount of NO₃^- was found in soil amended with inorganic fertilizer and vermicompost and the lowest in the soil amended with unlimed wastewater sludge. The concentration of NO₃^- in soil decreased when the soil water content increased in all treatments, except in the soil amended with unlimed wastewater sludge. It was found that water content affected the emission of CO₂ of N₂O and the concentration of NO₃^-, but not the amount of NH₄⁺ and NO₂^- in soil. Application of unlimed wastewater sludge increased the emissions of CO₂ and N₂O and the concentrations of NH₄⁺, but decreased the amount of NO₃^- in soil.